Method and device for decoding an incident pulse signal of the ultra wideband type, in particular for a wireless communication system

ABSTRACT

An incident pulse signal of the ultra wideband type conveys digital information that is coded using pulses having a known theoretical shape. A decoding device includes an input for receiving the incident signal, and for delivering a base signal. A comparator receives the base signal and delivers an intermediate signal representative of the sign of the base signal with respect to a reference. A sampling circuit samples the intermediate signal for delivering a digital signal. A digital processing circuit correlates the digital signal with a reference correlation signal corresponding to a theoretical base signal arising from the reception of a theoretical pulse having the known theoretical shape.

FIELD OF THE INVENTION

[0001] The present invention relates to radio frequency technology, andmore particularly, to the decoding of an incident pulse signal of theultra wideband type conveying coded digital information. The inventionadvantageously applies to the transmission of such information within alocal wireless transmission network.

BACKGROUND OF THE INVENTION

[0002] Ultra wideband technology is distinguished from narrowband andspread spectrum technologies in the sense that the bandwidth of an ultrawideband type signal is typically between about 25% to 100% of thecentral frequency. Moreover, instead of transmitting a continuouscarrier modulated with information or with information combined with aspreading code, which determines the bandwidth of the signal, ultrawideband technology involves transmission of a series of very narrowpulses. For example, these pulses may take the form of a single cyclehaving a pulse width of less than 1 ns. These pulses are extremely shortin the time domain, and when transformed into the frequency domain,produce the ultra wideband spectrum that is characteristic of UWBtechnology.

[0003] In UWB technology, the information on the signal can be coded,for example, by a modulation technique called pulse position modulation(PPM). In other words, the information coding is carried out by varyingthe instant of transmission of individual pulses. More specifically, thepulse train is transmitted at a frequency that can be as much as severaltens of MHz. Each pulse is transmitted in a window of predeterminedlength, such as 50 ns, for example. Compared to a theoretical positionof transmission, the pulse is then advanced or delayed, enabling a 0 ora 1 to be coded. More than two values can also be coded by using morethan two positions offset relative to the reference position. It is evenpossible to superimpose a BPSK modulation on this modulation.

[0004] On receipt of the transmitted signal, it is therefore necessaryto decode these pulses so as to determine the value of the digitalinformation conveyed. This decoding is essentially performed in ananalog manner by using an analog correlator. This requires a relativelycomplex hardware implementation. Moreover, the correlation system isassigned to a fixed position within each pulse transmission window.Consequently, the number of correlation chains must be equal to thenumber of position modulation levels.

[0005] Furthermore, such an architecture requires a precisesynchronization to find the right position modulation and the correctpolarity of the various symbols. This synchronization is performed byvery complex software, since only a limited number of observations arepossible. In addition, the precision of the clock, which is typically afew picoseconds, is a very constraining parameter. This is based uponthe technology and the current consumed using the technology.

SUMMARY OF THE INVENTION

[0006] The invention proposes a device for decoding an incident pulsesignal of the ultra wideband type conveying digital information codedusing pulses of a known theoretical shape.

[0007] According to a general characteristic of the invention, thedevice comprises input means for receiving the incident signal and fordelivering a base signal. The input means may include an antenna, forexample. Preprocessing means receive the base signal and delivers anintermediate signal representative of the sign of the base signal withrespect to a reference. The reference may be zero volts, for example.

[0008] The device preferably further comprises means of sampling theintermediate signal for delivering a digital signal, and digitalprocessing means comprising synchronization means and decoding means forcorrelating the digital signal with a reference correlation signal. Thereference correlation signal corresponds to a theoretical base signalarising from the reception of at least one theoretical pulse having theknown theoretical shape.

[0009] In other words, the invention enables an ultra wideband typepulse to be detected using the sign of the received signal, sampled andthen correlated with a predetermined digital correlation signal. Inaddition to the use of a binary signal representative of the sign of theincident signal for detecting pulses, the invention provides for all theprocessing to be carried out digitally, which simplifies the hardwareimplementation of the device. The processing, in particular, includesthe detection, synchronization and decoding of the pulses.

[0010] Furthermore, in the prior art, which uses an analog approach,either the information located outside of the instants of capture islost (for example, in the case of position modulation), or the pulsesare detected globally (for example, in the case of a BPSK modulation).However, according to the invention, it is possible to perform acontinuous sampling of the sign of the signal with a finer resolutionthan the width of the pulses, and to choose the best sampling instantsto carry out the digital processing, and in particular, the correlation.

[0011] In addition, in the wireless communication networks domain, theterminals generally use Rake receivers. A Rake receiver includes several“fingers” assigned to the various paths of a multi-path transmissionchannel. Therefore, when an analog approach is used for detecting UWBpulses, parts of the receive chain must then be duplicated as many timesas there are fingers.

[0012] However, according to the invention, the continuous sampling ofthe sign of the signal allows for a continuous observation of thesignal, and multiple paths can then be detected in a multi-pathenvironment without duplicating the receive chain. Moreover, accordingto the invention, the synchronization procedure is simplified incomparison to the algorithms proposed in the prior art. Specifically, byvirtue of the possibility of obtaining continuous observations, it isonly necessary to perform a correlation with a synchronization headercomprising a predetermined synchronization code.

[0013] According to an embodiment of the invention, the sampling meanscomprise serial-to-parallel conversion means for successively deliveringat a predetermined delivery frequency Fe, groups of N samples inparallel. This corresponds to an effective sampling frequency of theintermediate signal equal to N*Fe.

[0014] By way of example, when the pulses have a central frequency of afew GHz, the effective sampling frequency can be greater than 10 GHz. Inaddition, the fact that serial-to-parallel conversion means are usedallows a clock signal at a frequency Fe (for example, a few hundreds ofMHz) to be used, and an effective sampling frequency on the order of 20GHz or higher can be obtained. Current analog-to-digital converterscannot achieve this. N may be an integer power of 2, such as 7, forexample.

[0015] The serial-to-parallel conversion means advantageously comprise aprogrammable clock circuit receiving a base clock signal having thefrequency Fe and delivers N elementary clock signals all having the samefrequency Fe but temporally shifted by 1/N*Fe with respect to eachother. N flip-flops receive at their input the intermediate signal, andare respectively controlled by the N elementary clock signals. The Nflip-flops respectively deliver the N samples. The conversion meansfurther comprise an output register controlled by the base clock signalfor storing the N samples delivered by the N flip-flops, and fordelivering them in parallel at the delivery frequency.

[0016] The programmable clock circuit preferably comprises a digitalphase-locked loop including a programmable ring oscillator deliveringthe N elementary clock signals, and is controlled from a control circuitreceiving the respective outputs of N flip-flops. These N flip-flopsreceive the base clock signal and are respectively controlled by the Nelementary clock signals.

[0017] The use of a digital phase-locked loop combined with theserial-to-parallel conversion means allows a precision greater than afew tens of picoseconds to be obtained for the mutual phase shifts (inthe time domain) of the N elementary clock signals. Thus, according tothe invention, it is possible to detect the instant of arrival of apulse with a resolution equal to the precision of the N elementary clocksignals.

[0018] The sampling means, and in particular, the digital phase-lockedloop, are advantageously implemented in CMOS technology. In particular,this allows the sampling means and the digital processing means to beplaced in a standby mode for predetermined time intervals. In otherwords, the system can easily be switched on and off, resulting insignificant power savings.

[0019] According to an embodiment of the invention, the referencecorrelation signal is made up of reference samples. The digitalprocessing performed by the synchronization means and by the decodingmeans comprise a sliding correlation between the samples of the digitalsignal which are delivered by the sampling means and the referencesamples.

[0020] The information is conveyed within frames each comprising asynchronization header comprising at least one segment of length Tscontaining a synchronization code formed of several theoretical pulseshaving the known theoretical shape. The digital processing performed bythe synchronization means during the reception of a synchronizationheader then comprises, for example, a sliding correlation between N5reference samples and a set of N3 samples of a digital signal which aredelivered by the sampling means.

[0021] The N3 samples correspond to a signal duration greater than Ts insuch a way as to take account of an estimated length of the transmissionchannel. Moreover, in this synchronization phase, the N5 referencesamples correspond to a signal length Ts and to a theoretical basesignal arising from the reception of the synchronization code. Thesynchronization means then perform a detection of the synchronizationcode, possibly with circular permutations of this code, Qn the basis ofthe result of the correlation.

[0022] The result of the correlation may include detection of a maximum,or the detection of overshooting the reference threshold (0, forexample). Generally, the synchronization header comprises severalsegments of the same length Ts, each containing identicalsynchronization codes. The synchronization means then furthermorecomprise means for performing a series of coherent integrations of thedigital signal, thereby making it possible, in particular, to circumventnoise.

[0023] Although not indispensable, it is preferable for the device toalso comprise means for estimating the response of the transmissionchannel. The estimation means also perform a digital processingcomprising a correlation of the digital signal with the referencecorrelation signal. This makes it possible to have a good approximationof the response of the transmission channel, and this will subsequentlyfacilitate the decoding of the information.

[0024] Thus, according to an embodiment in which each frame furthermorecomprises a second part containing at least one pulse having a knownpolarity and a known time shift with respect to the synchronizationheader, the digital processing performed by the channel estimation meanscomprise a set of samples of the digital signal beginning at an instantseparated from the synchronization header by the time shift. The timeshift may be a predetermined number N4 of samples of the digital signalwhich are delivered by the sampling means. A sliding correlation isperformed between N2 reference samples and the set of N4 samples of thedigital signal for obtaining a vector of N4 reference correlationvalues. In this case, the N2 reference samples (N2=9, for example)correspond to a theoretical base signal arising from the reception of asingle theoretical pulse.

[0025] The second part of the frame may comprise several pulses having aknown polarity spaced regularly apart by time intervals corresponding toN4 samples of the digital signal. The channel estimation means thenpreferably further comprise means for performing a series of coherentintegrations of the digital signal. This also makes it possible tocircumvent noise. This vector of N4 reference correlation values willadvantageously be used in the decoding of the data.

[0026] More precisely, when the frame comprises a third part containingso-called “useful” pulses, that is, one which comprises information onthe final user of the wireless communication system, each pulse has aknown reference time position in the frame. The digital processingperformed by the decoding means advantageously comprise, beginning atthe assumed instant of reception of a useful current pulse, the storageof N4 samples of the digital signal. A sliding correlation between theN4 stored samples and the N2 reference samples obtain a vector of N4useful correlation values which are associated with this current usefulpulse. The comparison of this useful correlation vector with the vectorof N4 reference correlation values, or possibly when the pulses arecoded with a pulse position modulation (PPM) with this reference vectortemporally delayed or advanced by a predetermined shift are used in thePPM modulation.

[0027] The subject of the invention is also directed to a terminal of awireless communication system incorporating a decoding device as definedabove.

[0028] The subject of the invention is also directed to a method fordecoding an incident pulse signal of the ultra wideband type conveyingdigital information coded using pulses of a known theoretical shape. Themethod comprises at least one synchronization phase and decoding phase.The synchronization and decoding phases may be interleaved.

[0029] According to a general characteristic of the invention, thedecoding process comprises receiving the incident signal so as to obtaina base signal, and sampling an intermediate signal representative of thesign of the base signal with respect to a reference so as to obtain adigital signal. The synchronization phase and the decoding phasecomprise digital processing of the digital signal. This comprises acorrelation of the digital signal with a reference correlation signalcorresponding to a theoretical base signal arising from the reception ofat least one theoretical pulse having the known theoretical shape.

[0030] According to a mode of implementation, the sampling comprises aserial-to-parallel conversion for successively delivering at apredetermined delivery frequency Fe groups of N samples in parallel.This corresponds to an effective sampling frequency for the intermediatesignal equal to N*Fe. The pulses may have a central frequency of a fewGHz, for example. The effective sampling frequency may be greater than10 GHz. N may be an integer power of 2, and the effective samplingfrequency is, for example, on the order of 20 GHz. The deliveryfrequency Fe may be on the order of 200 MHz.

BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Other advantages and characteristics of the invention will becomeapparent on examining the detailed description of embodiments and modesof implementation, which are in no way limiting, and the appendeddrawings, in which,

[0032]FIG. 1 diagrammatically illustrates an incident signal of theultra wideband type in accordance with the present invention;

[0033]FIG. 2 illustrates in greater detail but again diagrammatically apulse position modulation (PPM) coding of a bit in accordance with thepresent invention;

[0034]FIG. 3 illustrates in greater detail one of the pulses of theincident signal of FIG. 1;

[0035]FIG. 4 illustrates in greater detail one of the pulses of the basesignal resulting from the reception of the incident signal by thereception system in accordance with the present invention;

[0036]FIG. 5 diagrammatically illustrates an embodiment of a detectiondevice in accordance with the present invention;

[0037]FIGS. 6 and 7 illustrate in greater detail but stilldiagrammatically an embodiment of the sampling means of the device ofFIG. 5;

[0038]FIG. 8 represents a timing chart of the various clock signals usedin the sampling means in accordance with the present invention;

[0039]FIG. 9 illustrates in greater detail, but still diagrammatically,an embodiment of the digital processing means of the device of FIG. 5;

[0040]FIG. 10 illustrates a reference correlation signal in accordancewith the present invention;

[0041]FIG. 11 diagrammatically illustrates the various functionsimplemented for decoding data conveyed within a transmission frame inaccordance with the present invention;

[0042]FIGS. 12 and 13 diagrammatically illustrate an implementation ofthe synchronization and an embodiment of the corresponding means using areference correlation signal such as, for example, the one illustratedin FIG. 10;

[0043]FIGS. 14 and 15 diagrammatically illustrate an implementation of achannel estimation and an embodiment of the corresponding means alsousing a reference correlation signal such as, for example, the oneillustrated in FIG. 10; and

[0044]FIG. 16 diagrammatically illustrates a mode of implementation ofthe data decoding in accordance with the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0045] In FIG. 1, the reference SGN designates an initial pulse signalof the ultra wideband type including pulses PLS having a knowntheoretical shape. More specifically, these pulses PLS have apredetermined time-domain width PW, which is typically less than 1 nsand on the order of 360 picoseconds, for example. The successive pulsesPLS are each contained in successive time windows of length T equal tothe inverse of the pulse repetition frequency (PRF). As a guide, thelength T of each time window is, for example, equal to 50 ns. Theposition of each pulse in a time window can vary from one window toanother according to a pseudo-random code. Moreover, when the signalcarries information coded using a pulse position modulation (PPM), thepulse can, as illustrated in FIG. 2, be slightly ahead (pav) or slightlydelayed (prt) relative to the reference position (pref) of the pulse inthe window, depending on the value 0 or 1 of the informationtransmitted.

[0046] The pulses PLS have characteristics of an ultra wideband typepulse in the sense that the ratio of the bandwidth of the pulse athalf-power to the central frequency is greater than ¼. As a guide, thecentral frequency of a pulse can vary between 2 and 4 GHz.

[0047] The detection device DDT according to the invention, anembodiment of which is illustrated in FIG. 5, enables the presence orabsence of pulses in the signal to be detected. When a pulse is present,the detection device DDT detects its instant of arrival and itspolarity. The device DDT particularly allows the decoding of the binarydata after having performed a synchronization and a channel estimation.This device can, for example, be incorporated in a terminal TRM of alocal area network type wireless communication system.

[0048] More specifically, this device DDT includes, in particular butnon-limited to the illustrated application, an antenna ANT to receivethe incident signal SGNR resulting from the transmission of the signalSGN over a transmission channel which may be a multi-path channel. Theantenna ANT forms the input means which delivers a base signal SGB fromthe incident signal SGNR. The base signal SGB is also a pulse signal ofthe ultra wideband type. After passing through the antenna ANT, theshape of the pulses PLSD making up this signal SGB is illustrated inFIG. 4. This shape is different from the shape of the pulses PLSillustrated in FIG. 3.

[0049] In other words, the pulse PLSD is the theoretical response of thesystem on receiving a pulse PLS. Of course, this theoretical responsevaries according to the characteristics of the reception means. The basesignal SGB is then amplified using low noise amplification means LNA.The output signal of the amplifier LNA is compared with a referencevoltage Vref (for example, 0 volts) in a comparator CMP. The comparatorCMP then delivers an intermediate signal SGI representative of the signof the base signal SGB, and consequently of the sign of the incidentsignal relative to the reference Vref.

[0050] The intermediate signal SGI is sampled in sampling means MECH.The sampling means MECH, as will be seen in more detail below, deliverssuccessive groups of N samples. All these samples are processed in thedigital processing means comprising correlation means for correlatingthe digital signal SNM delivered by the sampling means with apredetermined digital correlation signal SCR. The result of thiscorrelation enables the possible presence of a pulse to be detected, aswell as sychronization, channel estimation and decoding to be carriedout.

[0051] As the central frequency of the pulses of the signal can be onthe order of several GHz, the sampling frequency of the digital signalmust be very high, such as greater than 10 GHz, for example. A methodwhich is particularly straightforward to implement for sampling a signalat 10 GHz involves using serial-to-parallel conversion means, asillustrated in FIG. 6.

[0052] More specifically, the serial-to-parallel conversion means willsuccessively deliver at a predetermined delivery frequency Fe, forexample, on the order of 200 MHz, groups of N samples in parallel. Thiscorresponds to an effective sampling frequency of the intermediatesignal equal to N*Fe. Thus, N can be, for example, chosen to be equal to2^(m), where m may be equal to 7, and this leads to groups of 128samples being obtained. The effective sampling frequency will be greaterthan 20 GHz.

[0053] In terms of hardware, the serial-to-parallel conversion meanscomprise a programmable clock circuit CHP receiving a base clock signalCLKe having the frequency Fe and delivering N elementary clock signalsCLK1-CLKN all having the same frequency Fe but shifted temporally by1/N*Fe with respect to each other. Thus, as a guide, these clock signalsmay be shifted temporally with respect to each other by about 50picoseconds, for example.

[0054] The serial-to-parallel conversion means also comprise N D-typeflip-flops, respectively referenced FF1-FFN. These flip-flops arerespectively controlled by N elementary clock signals CLK1-CLKN, andthey all receive at their input the intermediate signal SGI from thecomparator CMP.

[0055] The intermediate signal SGI is sampled in synch with thesuccessive rising edges of the various elementary clock signalsCLK1-CLKN, and the N successive samples will be stored in an outputregister BF controlled by the base clock signal CLKe. At each risingedge of this base clock signal CLKe, the N samples will be delivered inparallel. The rising edges are spaced by an interval Te representing theperiod of the base clock signal.

[0056] By way of example, FIG. 8 can be referred to, in which, forsimplicity, only four elementary clock signals CLK1-CLK4 (correspondingto N=4) have been represented. As illustrated in FIG. 7, the base clocksignal CLKe is one of the elementary clock signals, such as, the signalCLK1, for example.

[0057] The programmable clock circuit CHP can be made up of a clock,such as, a quartz clock, for example, and a certain number of delayelements assembled in series at the output of the clock. To this end,the person skilled in the art may refer to European Patent ApplicationNo. 843,418.

[0058] One of the problems of this very high sampling frequency lies inthe fact that the elementary clock signals should be delivered with avery low jitter, for example, on the order of a few picoseconds. This isthe reason why it is therefore advantageous that the programmable clockcircuit CHP comprises a digital phase-locked loop comprising (FIG. 6),for example, a programmable ring oscillator OSC2 delivering the Nelementary clock signals CLK1-CLKN. This ring oscillator is controlledfrom a control circuit CCD receiving the respective outputs of Nflip-flops BS1-BSN. These N flip-flops are respectively controlled bythe N elementary clock signals CLK1-CLKN, and receive at their D inputthe base clock signal CLKe from a conventional quartz oscillator OSC1,for example.

[0059] To this end, the person skilled in the art may refer to U.S. Pat.No. 6,208,182 with respect to the control of the ring oscillator.Nevertheless, the general principles thereof will now be reviewed. Thecontrol circuit CCD comprise means for comparing samples in pairs, insuch a way as to determine if a state transition has occurred in aninterval of time separating the two samples. This comparison is madeover at least two cycles, which may be consecutive, of the ringoscillator.

[0060] This comparison is carried out in such a way that if during thesecond cycle a comparable state transition is detected in the sameinterval, the control of the ring oscillator is not modified. If duringthe second cycle a comparable state transition is detected in a laterinterval, the period of the ring oscillator is reduced. If during thesecond cycle a comparable state transition is detected in an earlierinterval, the period of the ring oscillator is increased.

[0061] Referring now to FIG. 9, the digital processing means MTNcomprise synchronization means MSYN, channel estimation means MEST anddecoding means for decoding the useful data MDCD. All these meansmoreover comprise correlation means MCORR for performing a digitalcorrelation of the signal delivered by the sampling means with areference correlation signal SCR.

[0062] In the described example, and because the pulses have a knownshape, the reference correlation signal is a reference signalcorresponding to the shape of a pulse after it has passed through theinput means. More specifically, as illustrated in FIG. 9, the digitalreference signal SCR may be, for example, a profile of nine samples forwhich the general shape corresponds to the general shape of a pulsePLSD. Each sample is separated in time by a distance Δt=1/N*Fe. Thereference signal SCR is therefore, in this case, a block of nine samplesrespectively having values 111-1-1111. As will be seen below, thereference signal SCR may correspond to several pulses PLSD, and includea larger number of samples. The correlation means MCORR performs asliding correlation between the digital signal samples delivered by thesampling means and the reference samples of the signal SCR.

[0063] Reference will now be made more particularly to FIG. 11 todescribe the synchronization, the channel estimation and decoding ofdata which is assumed to be conveyed within a frame TRA. This frame TRAcomprises a synchronization header ES having, for example, a duration onthe order of a few microseconds. The synchronization header ES issubdivided into several segments of identical length Ts, such as tensegments FRG1-FRG10, for example. Each segment FGR_(i) contains anidentical synchronization code CSY composed, for example, of sevenpulses having known positions and polarities.

[0064] In FIG. 11, the arrows of the code CSY designate the variouspulses together with their respective polarities. The length Tscorresponds to a set of N5 samples. The reference correlation signalthen comprises N5 samples corresponding to several pulses PLSD formingthe synchronization code.

[0065] In theory, it would be possible to acquire synchronization byusing a single set ES1 of N3 samples delivered by the sampling means(FIG. 12) by performing a sliding correlation between the N3 samples andthe N5 samples of the reference correlation signal SCR. Consequently, N3is greater than N5 and corresponds to a signal length greater than Ts,and may be equal to TS+L, where L is an estimated length for thetransmission channel.

[0066] The synchronization means MSYN will then detect the variousmaximums from among the correlation values, and this will make itpossible to detect the presence and the instant of arrival of the pulsesas well as their polarities according to the sign of these maximumvalues. Consequently, the means MSYN makes it possible to detect thesynchronization code CSY. As a variation, it is possible to detect justthe crossings through 0 of all of the correlation values.

[0067] It should be noted here that the synchronization code CSY will bedetected if the set of N3 samples over which the sliding correlation isperformed corresponds to a whole segment of the synchronization header.If, in contrast, this set of N3 samples straddles two consecutivesegments, then a circular permutation of the synchronization code willbe detected.

[0068] The signal SGNR which arrives on the antenna is noisy. This iswhy it is preferable for the synchronization means MSYN to furthermorecomprise means MIC (FIG. 9) for performing a series of coherentintegrations of the digital signal. Such coherent integrations areentirely known by a person skilled in the art. In the present case, asillustrated in FIG. 13, they include performing summations of commonsamples of the successive sets of N3 samples ES1-ES10 (corresponding interms of the number of samples to the length of the segments of thesynchronization header) so as to obtain in the end a final set ESF of N3samples on which the correlation means will perform the slidingcorrelation using the N5 reference samples.

[0069] This sliding correlation makes it possible, as indicated above,to detect the synchronization code CSY, possibly with the circularpermutations of this code. Once this detection has been performed, thesynchronization is acquired and it is then possible to go to the nextstep of the method which comprises performing an estimation of theimpulse response of the channel.

[0070] To determine the impulse response of the channel, the channelestimation means MEST will use a second part P2 (FIG. 11) of the frameTRA. This second part P2 in theory contains at least one pulse having aknown polarity and a known time shift t1 with respect to thesynchronization header. It contains several pulses of known polaritiesspaced regularly apart by a time interval t2 corresponding to N4 samplesof the digital signal.

[0071] The value N4 is chosen to correspond substantially to the lengthof the transmission channel, for example, on the order of 350nanoseconds. In theory, the presence of a single pulse in the part P2makes it possible to ascertain the impulse response of the channel.

[0072] More precisely, the estimation means MEST then stores, beginningat the instant t1 separated from the end of the synchronization header,which is known since the synchronization has been acquired previously,N4 samples of the digital signal which are delivered by the samplingmeans. The N4 samples represent the response of the channel to thetransmission of the pulse which was sent after a duration t1 after theend of the synchronization header.

[0073] As illustrated in FIG. 14, the correlation means of theestimation means performs a sliding correlation between the set ES11 ofthe N4 stored samples and the N2 reference samples of the referencecorrelation signal SCR of FIG. 10. This makes it possible to obtain areference correlation vector having N4 reference correlation values, andit is this vector of the N4 reference correlation values whichrepresents the impulse response of the channel.

[0074] More precisely, since N2 is typically much less than N, thecorrelation means will first perform a first correlation (which is aterm by term multiplication) between the N2 reference samples and thefirst N2 samples of the group of N samples delivered by the samplingmeans. This will give a first correlation value. Then, every Δt, the N2reference samples will be shifted by one sample so as to obtain a newcorrelation value. Also, this sliding correlation will be performed onthe set ESll of N4 samples of the digital signal.

[0075] As already indicated above, and since the signal SGNR whicharrives at the antenna is noisy, it is preferable for the estimationmeans to be provided with means MIC for performing a series of coherentintegrations of the digital signal. More precisely, as illustrated inFIG. 15, and by analogy with FIG. 13, the means MIC of the estimationmeans MEST performs summations of common samples of all the setsES11-ES51 of N4 samples forming the second part P2 of the frame TRA.This is done to obtain a final set ESF of N4 samples over which thecorrelation means will carry out the sliding correlation with thereference correlation signal SCR. This is done to obtain the referencecorrelation vector having N4 reference correlation values. The decodingmeans MDCD will then carry out the decoding of the information containedin the third part P3 of the frame TRA by using the vector of the N4reference correlation values.

[0076] More precisely, this third part P3 of the frame, which issituated ahead of the terminal part P4 of this frame, comprises socalled “useful” pulses which will code the useful data to betransmitted. In FIG. 11, just as for the synchronization code CSY andthe second part P2, the arrows designate the reference positions pref(FIG. 2) of the pulses in a PPM modulation. Also, the time shift t3existing between the end of the second part P2 of the frame and thefirst useful pulse is known very precisely, as are the various timeshifts t4 and t5 separating the following pulses.

[0077] Thereafter, the digital processing performed by the decodingmeans MDCD comprise, beginning at the assumed instant of reception of acurrent useful pulse, the storage of N4 samples of the digital signaldelivered by the sampling means. Then, the correlation means MCORR ofthese decoding means MDCD performs a sliding correlation between the N4stored samples and the N2 reference samples (FIG. 16) to obtain a vectorof N4 useful correlation values which is associated with this currentuseful pulse.

[0078] Then, the means MDCD compares the useful correlation vector withthe vector of N4 reference correlation values temporally delayed ortemporally advanced by the shift provided for in a PPM modulation so asto determine the 0 or 1 value of the data item thus coded.

[0079] In terms of hardware, the sampling means and the digitalprocessing means can be implemented in CMOS technology, which isbeneficial in terms of manufacturing costs. This technology can also beused to provide control means MCTL (FIG. 5) for placing the samplingmeans and/or the correlation means in a standby state, for example,during periods of time when the system knows it is not receiving anypulses, or even during periods when the signal/noise ratio is notoptimal. This leads to an appreciable power savings. Furthermore, thecorrelation means can be implemented by several correlators in parallelfor processing in parallel several groups of N samples so as to obtain aprocessing speed compatible with the effective sampling frequency equalto N*Fe.

[0080] It is also conceivable to perform coherent integrations duringthe decoding phase if each item of useful information is spread overseveral pulses. Finally, as far as the coherent integrations aregenerally concerned, should the successive pulses be spaced apartirregularly in time (for example, according to a known code), thesummations of samples c43qan take the time shift between the pulses intoaccount.

That which is claimed is:
 1. Method for decoding an incident pulsesignal of the ultra wideband type conveying digital information codedusing pulses of known theoretical shape, comprising at least onesynchronization phase and one decoding phase, characterized in that itcomprises a reception of the incident signal so as to obtain a basesignal (SB), and a sampling of an intermediate signal (SI)representative of the sign of the base signal with respect to areference, so as to obtain a digital signal (SNM), and in that thesynchronization phase and the decoding phase comprise digitalprocessings of the digital signal comprising a correlation of thedigital signal with a reference correlation signal (SCR) correspondingto a theoretical base signal arising from the reception of at least onetheoretical pulse having the said known theoretical shape.
 2. Methodaccording to claim 1, characterized in that the sampling comprises aserial-to-parallel conversion in such a way as to successively deliverat a predetermined delivery frequency Fe, groups of N samples inparallel, which corresponds to an effective frequency of sampling of theintermediate signal (SI) equal to N.Fe.
 3. Method according to claim 2,characterized in that the pulses (PLSD) have a central frequency of afew GHz, and in that the effective sampling frequency is greater than 10GHz.
 4. Method according to claim 3, characterized in that N is aninteger power of 2, and in that the effective sampling frequency is ofthe order of 20 GHz, the delivery frequency Fe being of the order of 200MHz.
 5. Method according to one of the preceding claims, characterizedin that the reference correlation signal (SCR) is formed of referencesamples, and in that the digital processings performed in thesynchronization phase and in the decoding phase comprise a slidingcorrelation between the samples of the digital signal and the referencesamples.
 6. Method according to claim 5, characterized in that theinformation is conveyed within frames (TRA) each comprising asynchronization header (ES) comprising at least one segment (FRGI) oflength Ts containing a synchronization code (CSY) formed of severaltheoretical pulses, in that the reference signal is formed of N5 samplescorresponding to a signal duration equal to Ts and to a theoretical basesignal arising from the reception of the synchronization code, and inthat the digital processing performed in the synchronization phaseduring the reception of a synchronization header comprises a slidingcorrelation between the N5 reference samples and a set of N3 samples ofthe digital signal corresponding to a signal duration greater than Ts,and a detection of the synchronization code possibly with circularpermutations of this code on the basis of the result of the correlation.7. Method according to claim 6, characterized in that thesynchronization header comprises several segments (FRGI) of the samelength Ts each containing identical synchronization codes, and in thatthe digital synchronization processing furthermore comprises a series ofcoherent integrations of the digital signal.
 8. Method according to oneof claims 1 to 5, characterized in that it furthermore comprises a phaseof estimating the response of the transmission channel also comprising adigital processing comprising a correlation of the digital signal withthe reference correlation signal (SCR).
 9. Method according to claim 8,characterized in that the information is conveyed within frames (TRA)each comprising a synchronization header (ES) and a second part (P2)containing at least one pulse having a known polarity and known timeshift (t1) with respect to the synchronization header, in that thereference correlation signal (SCR) is formed of N2 samples correspondingto a theoretical base signal arising from the reception of a singletheoretical pulse, and in that the digital processing performed in thechannel estimation phase comprises the storage beginning at an instantseparated from the synchronization header by the said time shift, of apredetermined number N4 of samples of the digital signal, and a slidingcorrelation between the N2 reference samples and the set of N4 samplesof the digital signal, so as to obtain a vector of N4 referencecorrelation values.
 10. Method according to claim 9, characterized inthat the second part of the frame (P2) comprises several pulses of knownpolarity spaced regularly apart by a time interval (t2) corresponding toN4 samples of the digital signal, and in that the digital processingperformed in the channel estimation phase furthermore comprises a seriesof coherent integrations of the digital signal.
 11. Method according toone of claims 9 and 10, characterized in that the frame comprises athird part (P3) containing so-called useful pulses coding useful data,each pulse having a known reference time position in the frame, and inthat the digital processing performed in the decoding phase comprises,beginning at the assumed instant of reception of a current useful pulse,the storage of N4 samples of the digital signal, a sliding correlationbetween the N4 stored samples and the N2 reference samples so as toobtain a vector of N4 useful correlation values which is associated withthis current useful pulse, and the comparison of this useful correlationvector with the vector of N4 reference correlation values, or possiblywith this reference vector temporally delayed or advanced by apredetermined shift.
 12. Device for decoding an incident pulse signal ofthe ultra wideband type conveying digital information coded using pulsesof known theoretical shape, characterized in that it comprises inputmeans (ANT) for receiving the incident signal and delivering a basesignal, preprocessing means (CMP) receiving the base signal and suitablefor delivering an intermediate signal representative of the sign of thebase signal with respect to a reference, means (MECH) of sampling theintermediate signal suitable for delivering a digital signal, anddigital processing means (MTN) comprising synchronization means (MSYN)and decoding means (MDCD) suitable for performing a correlation of thedigital signal with a reference correlation signal corresponding to atheoretical base signal arising from the reception of at least onetheoretical pulse having the said known theoretical shape.
 13. Deviceaccording to claim 12, characterized in that the sampling means (MECH)comprise serial-to-parallel conversion means suitable for successivelydelivering at a predetermined delivery frequency Fe, groups of N samplesin parallel, which corresponds to a virtual frequency of sampling of theintermediate signal equal to N.Fe.
 14. Device according to claim 13,characterized in that the serial-to-parallel conversion means comprise aprogrammable clock circuit (CHP) receiving a base clock signal havingthe frequency Fe and delivering N elementary clock signals all havingthe same frequency Fe but temporally shifted by 1/N.Fe with respect toeach other, N flip-flops all receiving at the input the intermediatesignal, respectively controlled by the N elementary clock signals, andrespectively delivering the N samples, an output register controlled bythe base clock signal to store the N samples delivered by the Nflip-flops and deliver them in parallel at the delivery frequency. 15.Device according to claim 14, characterized in that the programmableclock circuit (CHP) comprises a digital phase-locked loop including aprogrammable ring oscillator (OSC2) delivering the N elementary clocksignals and controlled from a control circuit receiving the respectiveoutputs of N flip-flops all receiving the base clock signal andrespectively controlled by the N elementary clock signals.
 16. Deviceaccording to one of claims 13 to 15, characterized in that the pulseshave a central frequency of a few GHz, and in that the effectivesampling frequency is greater than 10 GHz.
 17. Device according to claim16, characterized in that N is an integer power of 2, and in that theeffective sampling frequency is of the order of 20 GHz, the deliveryfrequency Fe being of the order of 200 MHz.
 18. Device according to oneof claims 12 to 17, characterized in that the sampling means (MECH) areimplemented in CMOS technology.
 19. Device according to claim 18,characterized in that it includes control means (MCTL) intended to placethe sampling means and the digital processing means into a standby modeduring predetermined time intervals.
 20. Device according to one ofclaims 12 to 19, characterized in that the reference correlation signal(SCR) is formed of reference samples, and in that the digitalprocessings performed by the synchronization means and by the decodingmeans comprise a sliding correlation between the samples of the digitalsignal and the reference samples.
 21. Device according to claim 20,characterized in that the information is conveyed within frames eachcomprising a synchronization header (ES) comprising at least one segment(FRGI) of length Ts containing a synchronization code formed of severaltheoretical pulses, in that the reference correlation signal (SCR) isformed of N5 samples corresponding to a signal duration equal to Ts andto a theoretical base signal arising from the reception of thesynchronization code (CSY), and in that the digital processing performedby the synchronization means during the reception of a synchronizationheader comprises a sliding correlation between the N5 reference samplesand a set of N3 samples of the digital signal corresponding to a signalduration greater than Ts, and a detection of the synchronization codepossibly with circular permutations of this code on the basis of theresult of the correlation.
 22. Device according to claim 21,characterized in that the synchronization header (ES) comprises severalsegments (FRGI) of the same length Ts each containing identicalsynchronization codes, and in that the synchronization means furthermorecomprise means suitable for performing a series of coherent integrationsof the digital signal.
 23. Device according to one of claims 12 to 20,characterized in that it furthermore comprises means for estimating theresponse of the transmission channel (MEST) suitable for also performinga digital processing comprising a correlation of the digital signal withthe reference correlation signal.
 24. Device according to claim 23,characterized in that the information is conveyed within frames (TRA)each comprising a synchronization header (ES) and a second part (P2)containing at least one pulse having a known polarity and known timeshift with respect to the synchronization header, in that the referencecorrelation signal (SCR) is formed of N2 samples corresponding to atheoretical base signal arising from the reception of a singletheoretical pulse, and in that the digital processing performed by thechannel estimation means comprises the storage beginning at an instantseparated from the synchronization header by the said time shift, of apredetermined number N4 of samples of the digital signal, and a slidingcorrelation between the N2 reference samples and the set of N4 samplesof the digital signal, so as to obtain a vector of N4 referencecorrelation values.
 25. Device according to claim 24, characterized inthat the second part of the frame (P2) comprises several pulses of knownpolarity spaced regularly apart by a time interval corresponding to N4samples of the digital signal, and in that the channel estimation meansfurthermore comprise means suitable for performing a series of coherentintegrations of the digital signal.
 26. Device according to one ofclaims 24 and 25, characterized in that the frame comprises a third part(P3) containing so-called useful pulses coding useful data, each pulsehaving a known reference time position in the frame, and in that thedigital processing performed by the decoding means comprises, beginningat the assumed instant of reception of a current useful pulse, thestorage of N4 samples of the digital signal, a sliding correlationbetween the N4 stored samples and the N2 reference samples so as toobtain a vector of N4 useful correlation values which is associated withthis current useful pulse, and the comparison of this useful correlationvector with the vector of N4 reference correlation values, or possiblywith this reference vector temporally delayed or advanced by apredetermined shift.
 27. Terminal of a wireless transmission system, forexample of the local network type, characterized in that it incorporatesa device according to one of claims 12 to 26.